V. A. Arbuzov

Observation of large-scale hydrodynamic structures in a vortex tube and the Ranque effect

The existence of large-scale structures in the form of a vortical double helix in a swirling Ranque flow is observed for the first time. The structure of the vortical double helix is visualized in real time by the method of Hilbert bichromatic filtering. The experimental result is interpreted on the basis that the most probable physical mechanism for the spatial energy separation in the gas flow (i.e., for the so-called Ranque effect) is viscous heating of the gas in a thin boundary layer at the walls of the vortex chamber and the adiabatic cooling at the center owing to the formation of an intense vortex braid near the axis.

Optical diagnostics of the structure and evolution of buoyant jets in a high-viscosity fluid

The structure and evolution of thermogravitational buoyant jets in a high-viscosity fluid above a linear source of heat suddenly switched on are studied by methods of the Hilbert optics and interferometry. Such jets can be considered as a model of an upward flow in the spreading zone in geodynamic problems associated with the behavior of the Earth’s mantle at large depths. Based on the interferogram structure, three-dimensional reconstruction of the temperature field in the jet is performed. The Hilbert image of the reconstructed three-dimensional temperature field is compared with the Hilbert image and interferogram of the jet.

Hilbert diagnostics of phase disturbances of the light field induced by a vortex flow

Methods of Hilbert filtration of phase disturbances of the light field in the spectral range of source emission are discussed. The evolution of complementary vortex rings induced in an air medium by a pressure pulse on the hole in the combustor wall under various boundary and initial conditions is experimentally studied.

Experimental and numerical study of nonstationary buoyant jets

The origin and development of buoyant jets over a sudden linear heat source in a highly viscous fluid with a Prandtl number equal to 2700 are experimentally and numerically studied. The time evolutions of the spatial flow form and temperature and velocity fields are investigated as functions of power supply.

Hilbert diagnostics of Rayleigh-Benard convection in fluids

An combined optical and thermal imaging experimental system was designed to investigate Rayleigh-Benard convection of a fluid in a layer with two rigid isothermal boundaries and a free upper boundary under steady and unsteady thermal boundary conditions. The fluid surface structure was visualized using methods of reflected-light Hilbert optics. Noncontact control of the fluid layer thickness was performed using a specially designed remote meter based on an MBR-1 microscope with a smooth focusing unit based on the Meyer mechanism. The evolution of the dynamic structure of the surface and temperature field of the fluid being analyzed were studied experimentally, and the existence of flows in the form of two-dimensional rolls with axes of rotation parallel to the lateral boundaries (the walls of the cavity) was confirmed. It is shown that the highly viscous fluid flow has a thermal gravitational nature. Correspondence is found between the evolution of the thermograms and Hilbert schlieren patterns of surface structures in different modes of Rayleigh-Benard convection.

Hilbert-diagnostics of vortex rings induced in air by a pressure pulse on a hole

Formation and evolution of complementary vortical rings induced in air by a pressure pulse on a hole under various boundary conditions are investigated by Hilbert-optics methods and computer modeling. It is experimentally demonstrated that reverse ring-shaped vortices inside the chamber after its depressurization are formed not only in the case with a reduced initial pressure in the chamber as compared with the ambient atmospheric pressure but also in the case with a higher gas pressure in the chamber than the atmospheric pressure. The complementary vortex rings propagating in forward and reverse directions might significantly affect the combustion process in the jets.

Optical Hilbert diagnostics of dynamic structures in gas flows

The possibility of visualizing the fine structure of optical inhomogeneities in gas and condensed fluids by Hilbert optics methods is discussed. Application of optical Hilbert filtering for investigating shock waves and dynamic perturbations induced by the waves in gas is described.

Regimes of Unstable Expansion and Diffusion Combustion of a Hydrocarbon Fuel Jet

Results of an experimental study of hydrodynamics and diffusion combustion of hydrocarbon jets are presented. Various regimes of instability development both in the jet flame proper and inside the source of the fuel jet are considered. The experiments are performed for the case of subsonic gas jet expansion into the air from a long tube 3.2 mm in diameter in the range of Reynolds numbers from 200 to 13 500. The fuel is the propane–butane mixture in experiments with a cold jet (without combustion) and pure propane or propane mixed with an inert dilutant (CO2 or He) for the jet flame. The mean velocity and velocity fluctuations in the near field of the jet without combustion are measured. Among four possible regimes of cold jet expansion (dissipative, laminar, transitional, and turbulent), three last regimes are investigated. The Hilbert visualization of the reacting flow is performed. The temperature profiles in the near field of the jet are measured by a Pt/Pt–Rh thermocouple. An attached laminar flame is observed in the transitional regime of propane jet expansion from the tube. In the case of combustion of C3H8 mixtures with CO2 or with He in the range of Reynolds numbers from 1900 to 3500, the transitional regime is detected in the lifted flame. Turbulent spots formed in the tube in the transitional regime exert a significant effect on the flame front position: they can either initiate a transition to a turbulent flame or lead to its laminarization.

Optical Hilbert diagnostics of convective structures and phase transition in a horizontal layer of supercooled water

Methods of Hilbert optics are used to visualize evolution of convective structures and wave front of crystallization in a horizontal layer of supercooled water bounded by thermally stabilized plane surfaces. Measured phase velocities and shapes of the crystallization front approximated with the aid of the Bezier curves are presented. The spatiotemporal quasi-periodicity of the phase-velocity field can be related to oscillatory modes of the crystallization front as a dynamic surface of the water–ice interphase transition.

Dynamics of the crystallization front induced by the temperature gradient at the upper boundary of a horizontal layer of a fluid

The dynamics of the crystallization front induced by the temperature gradient at the upper boundary of a horizontal layer of water bounded by flat thermostatted surfaces is studied. The formation and evolution of convective structures are visualized by methods of the Hilbert optics and digital video recording. The difference in the temperatures of the upper (T1) and lower (T2) thermostats satisfies the condition T1 < T2. In this system, the temperature of the cooled upper surface is an order parameter. Reaching a critical value of this parameter leads to a bifurcation phase transition from the liquid state (supercooled water) to the solid state (ice). The velocity and shape of the crystallization wave front are determined. The spatial-temporal state of the crystallization wave is found, in which the wave front shape is a line of equal velocities. The dynamic profile of the isothermal surface bounding the spatial shape of the solid phase is visualized.